Manufacture of unoxidisable timepiece springs



United States Patent MAYUFACTURE OF UNOXIDISABLE TIMEPIECE SPRINGS Ernest Dnbois, La Chaux de Fonds, and Bruno Siegrist and Charles Wakker, Geneva, Switzerland No Drawing. Application March 27, 1951,

Serial No. 217,872 7 Claims priority, application Switzerland May 12, 1949 2 Claims. (Cl. 75-134) This application is a continuation-in-part of our copending application Serial No. 154,006 filed April 4, 1950, now abandoned.

One of the most frequent causes of stoppage of watches and small clocks is the breaking of the main spring or barrel spring. This breakage is caused either by fatigue of the metal, in the strict sense of the term, or by localised corrosions.

For the manufacture of timepiece springs, hardened and tempered carbon steel has heretofore been used almost exclusively, having been hitherto regarded as the metal capable of storing most work Within the small available volume of the barrel. However, carbon steel of the kind used has only slight resistance to fatigue and is subject to intercrystalline corrosion and to rust.

The timepiece spring according to this invention, the shape and dimensions of which may be the same as those of normal springs, consists of an unoxidisable alloy, which, with the same bulk, stores substantially the same amount of Work and supplies the same torque as a steel spring, but has a much greater resistance to fatigue and under normal conditions is completely resistant to corrosion and oxidation.

These advantages are obtained by the use of an unoxidisable alloy of cobalt, nickel and iron, with .or without chromium, tungsten, molybdenum or tantalum, characterised by the addition, as a hardening element, of columbium and titanium acting together. Such an alloy is brought to a soft state by being heated to a high temperature followed by rapid quenching and is hardened by heat treatment at a suitable temperature. It is generally recognized that in the soft state the constituents of the alloy are in solid solution, while in the hardened state some of the constituents are in a form which is insoluble in the base metal. The alloy can be worked in the soft state and can be hardened by a precipitation heat treatment, the efiect of which is not restricted to the surface and which does not cause deformation as in the case of carbon steel.

After being dissolved by one or more heat treatments between ll00 and 1250" C. in the course of the manufacture of the alloy, this hardening element, columbium and titanium, imparts to the alloy, for instance by means of the final tempering treatment described hereinafter, a very high elastic limit and resistance to fatigue, very much greater than would be obtained by the use of only one of these two metals.

The Curie point of this alloy may be displaced below the ambient temperature by the addition of a suificient quantity of chromium, which does not substantially modify the above-mentioned properties, and thus renders it non-magnetic. Carbon which may be present as an impurity does not, as such, impair the qualities of the alloy- The structure is ferritic or austenitic, depending on the proportions of nickel and of chromium.

Such a spring does not present difliculties in manufacture; any heat treatment from 5 minutes to two hours ICC between 500 and 700 hardens it considerablyand increases the initial Vickers hardness of the alloy by more than kg./mrn.

The temperature and duration of the heat treatment may vary within wide limits; the duration may be made such as to enable the spring to be fixed in the desired form and at the same time to obtain optimum hardening. Numerous tests have enabled the following alloy composition limits to be established:

Percent Cobalt 20 to 45 Nickel 20 to 35 Iron 10 to 25 Titanium 1 to 5 Columbium l to 5 Chromium Up to 20 Tungsten Up to 10 Molybdenum Up to 10 Tantalum Up to 5 Percent Nickel 21 Cobalt 34 Iron 19 Chromium 14 Molybdenum 6 Titanium 2.5 Columbium 2.5 Tantalum 0.5 Manganese 0.5

and hardened by treatment for 1 hour at 520 C. supply torque and work substantially equal to those supplied by a spring of the same dimensions and consisting of steel of the highest quality, but have from four to seven times as much resistance to fatigue and very satisfactory resistance to corrosion.

Such a spring undergoes no permanent deformation during operation and its form in a free position after the first winding or other stressing is substantially retained until breakage.

The great resistance to corrosion and to fatigue possessed by this spring arise on the one hand from the alloy composition itself and on the other hand from the fact that in contradistinction to the hardening of carbon steel the hardening heat treatment brings the components of the alloy into a state of structural equilibrium, equalising within the metal the internal stresses to which its is necessarily subjected.

Although the spring to which this invention relates is intended primarily for use in the movements of watches and small clocks, it may be used without substantial modification, with all of the above-mentioned advantages, in any other timepiece movement, independently of whether the winding or other stressing is effected by hand or automatically, and also in the movements of measuring, inspecting and delayed-action devices.

This new spring has much greater endurance than the best steel springs, and avoids breakages due to rust and corrosion, these advantages being obtained without re duction of the force developed or of the work stored within a given volume and without modification of the dimensions of the barrel.

.3 'What we claim is:

1. An 'unoxidisable' timepiece mainspring with high resistance to fatigue consisting of a thin ribbon formed of an alloy containing:

I 10'-25%;i ofr'iron 15% of titanium 1-5% of colunrbium Up to 10%11of tungsten Up to 10%: of molybdenum Up to 20% of chromium Up to -.5% of: tantalum Rest Of-. Cbbflltl: and nickel,

the "nickel content being in the limits of 25-35%, the cobalt'content'being in"the"limits"of"2045% of the to- 'tal'weight and the 'content of "columbium and titanium jtog'ether being'atleastequal to 3% and not exceeding 7%, saidalloy' beinghardened'andthe components of the alloy being in "a' 'state'of structural equilibrium.

2: In a process" for" manufacturing an unoxidisable timepiece mainspring"with"'high resistance to fatigue, 'the 'steps of'forming a"'mainspring of an alloy containmg:

10-25% of iron 1-5% of-titanium 1-5%- ofcolumbium Up to 10% of tungsten Up to 10% o molybdenum Up tol20% of chrouim Up: to oftantalum Rest of cobalt and nickel,

the nickel content being in the limits of 20-35%, the cobalt content being in" the limits of 20-45% of the total weight and the content of columbium and titanium together being at least equal to 3% and not exceeding 7%; subjecting the alloy, in the course of manufacture, to at least one heat treatmentbetween 1100 and 1250' C., followed by quenching and tota final hardening heat treatment at a 'mediurn temperature between 500 and 700 C., the duration of said final hardening heat treatment being .from 5 minutes to2 hours.

References Cited in the file of this patent UNITEDiSTATES PATENTS FOREIGN PATENTS Material and Methods, High Strength Nickel Alloy Retains-Performance Properties at High Temperatures, October 1949, pp. 57-61. 

1. AN UNOXIDISABLE TIMEPIECE MAINSPRING WITH HIGH RESISTANCE TO FATIGUE CONSISTING OF A THIN RIBBON FORMED OF AN ALLOY CONTAINING: 10-25% OF IRON 1-5% OF TITANIUM 1-5% OF COLUMBIUM UP TO 10% OF TUNGSTEN UP TO 10% OF MOLYBDENUM UP TO 20% OF CHROMIUM UP TO 5% OF TANTALUM REST OF COBALT AND NICKEL, THE NICKEL CONTENT BEING IN THE LIMITS OF 25-35%, THE COBALT CONTENT BEING IN THE LIMITS OF 20-45% OF THE TOTAL WEIGHT AND THE CONTENT OF COLUMBIUM AND TITANIUM TOGETHER BEING AT LEAST EQUAL TO 3% AND NOT EXCEEDING 7%, SAID ALLOY BEING HARDENED AND THE COMPONENTS OF THE ALLOY BEING IN A STATE OF STRUCTURAL EQUILIBRIUM. 